This nonprovisional application claims priority under 35 U.S.C. xc2xa7 119(a) on Patent Application No. 2001-3511177 filed in Japan on Nov. 16, 2001, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a fuel injection apparatus capable of improving mileage by reducing return fuel and leak fuel while excellently maintaining a shape of an injection rate waveform.
2. Description of Related Art
A common rail type fuel injection apparatus is known as a fuel injection apparatus of a diesel engine. According to such a common rail type fuel injection apparatus, injection pressure and injection timing can be controlled independently from each other. Thus, the common rail type fuel injection apparatus is becoming a mainstream as an injection system of a diesel engine for an automobile. However, according to a conventional common rail type fuel injection apparatus, a timing of closing a control valve (first control valve) for controlling to start and stop fuel injection by the injector and a timing of closing a control valve (second control valve) for controlling to supply and stop high pressure fuel to the injector are made to coincide with each other so as to provide the stable injection rate waveform. If necessary, the timing of closing the second control valve is retarded with respect to the timing of closing the first control valve.
This signifies that a time period in which high pressure fuel acts on the injector and the like is prolonged. Therefore, leak fuel or return fuel is increased. The leak fuel is a small amount of fuel leaked out from a seal portion of the injector when the high pressure fuel acts on the injector. The return fuel is a fuel returned from the common rail to a fuel tank without contributing to fuel injection.
The increase in the leak fuel or the return fuel signifies an increase in an amount of driving work of a fuel supply pump for supplying fuel to the common rail. As a result, the engine for driving the fuel supply pump is obliged to carry out unnecessary work, constituting a factor of a deterioration in fuel consumption.
The invention resolves such a problem and it is an object thereof to provide a fuel injection apparatus capable of reducing return fuel or leak fuel while excellently maintaining a shape of an injection rate waveform to thereby improve mileage.
A fuel injection apparatus of an engine according to the invention includes: a high pressure fuel source capable of supplying a high pressure fuel; a low pressure fuel source capable of supplying a fuel at a pressure lower than a fuel pressure of the high pressure fuel source; switching means; an injector connected to the high pressure fuel source and the low pressure fuel source via the switching means; and controlling means for controlling switching of the fuel sources by the switching means and operation of the injector; wherein the controlling means switches the fuel source for supplying the fuel to the injector from the high pressure fuel source to the low pressure fuel source a predetermined time period earlier from a point of time when the injector finishes an injection of the high pressure fuel.
Since a timing of switching the switching means for selecting either one of the high pressure fuel source and the low pressure fuel source so as to communicate to the injector is set to be earlier than a point of time when the injector finishes the fuel injection, a time period in which high pressure fuel acts on the injector is shortened to thereby reduce leak fuel. In the case of a fuel injection apparatus of a two common rails type, a time period in which high pressure acts on a low-pressure common rail is shortened to thereby reduce return fuel. The leak fuel or the return fuel is reduced in this way and therefore, wasteful supply of fuel to the high pressure fuel source or the low pressure fuel source can be restrained and load of the engine can be reduced to thereby improve mileage.